Finally we come to the type of fluid which will be of most interest to us. A perfect fluid in Special Relativity is defined to be a fluid that has no heat conduction in the MCRF. It is the generalization of the ideal gas in ordinary thermodynamics. In the MCRF the components of are
It is easy to show that in a general frame we have [ Assignment 4 ]:
This is the energy- momentum tensor of a perfect fluid.